1. Field of the Invention
The present invention relates to an apparatus for steam reforming to convert hydrocarbons such as methane into hydrogen, ammonia, methanol, oxo gas, town gas, etc. More particularly, it is concerned with a hydrocarbon reforming apparatus which has a high thermal efficiency, is compact in size, and saves the cost of reforming catalysts.
2. Description of the Prior Art
There are several known reforming apparatuses for converting hydrocarbons (such as fuel oil, naphtha, and natural oil) into reformed gas, which is a combustible gas composed of hydrogen as a principal component and carbon monoxide, carbon dioxide, and methane by mixing the feedstock with steam and passing the mixture through a catalyst layer. They are disclosed in Japanese Patent Laid-open Nos. 78992/1978, 79766/1978, 90862/1981, and 63783/1983, and Japanese Patent Publication No. 7538/1982. They are of double-pipe structure in which the hydrocarbon feedstock for reforming is passed through a reaction tube which is filled with a catalyst and heated externally by a combustion gas from a burner. The double-pipe structure improves the thermal efficiency and makes the apparatus compact.
There is another known reforming apparatus disclosed in Japanese Patent Laid-open No. 102801/1984. It is made up of a reactor of triple-pipe structure and a combustion chamber surrounding the reactor. It is designed such that the combustion gas from the combustion chamber passes through the central tube of the reactor and the feedstock passes through the middle tube and then the outer tube in the direction opposite to that in which the combustion gas flows. While passing through the reactor, the feedstock receives the heat necessary for steam reforming which is an endothermic reaction.
The above-mentioned reforming apparatus, however, is not satisfactory in performance. It is poor in thermal efficiency as indicated by the fact that it discharges the exhaust gas at a considerably high temperature. It does not heat the reactor uniformly, nor does it utilize the heat of the combustion gas efficiently. Furthermore, it is not compact because it needs a thick insulation layer.